Plasma discharges can be used to excite gases to produce activated gases containing ions, free radicals, atoms and molecules. Activated gases are used in numerous industrial and scientific applications including processing solid materials such as semiconductor wafers, powders, and other gases.
Plasma can be generated in various ways including DC discharge, RF discharge, and microwave discharge. RF discharges produce high energy ions and, therefore, are often used to generate plasmas for applications where the material being processed comes into contact with the plasma. RF discharges can be achieved by electrostatically or inductively coupling energy from a power supply to a plasma. Inductively-coupled plasma generators typically employ complex power delivery systems. In addition, precision instrumentation is usually required to ascertain and/or control the power reaching the plasma.
Various approaches exist for ascertaining and/or controlling power reaching the plasma in an inductively-coupled plasma generator. For example, some approaches estimate plasma power using input voltage supplied to the plasma and/or current in the primary winding of the transformer for generating plasma. Existing approaches for determining parameters of plasmas produced in inductively-coupled plasma generators typically focus on either the primary-side or the secondary-side coils of the inductive element. One problem with existing approaches is a failure to provide direct or precise measurements of power delivered to the plasma, in part due to the distance of the measurement equipment from the inductive element and/or the presence of intervening elements. Another potential problem is failure of existing techniques to accurately estimate or characterize plasma resistance, due in part, again, to the distance of the measurement equipment from the inductive-element. Because plasma power and plasma resistance can be used to accurately and efficiently control power delivery to the plasma, ensure repeatability of the process for plasma generation, and diagnose process-related issues, better techniques for measuring and controlling functionality of plasma generators are needed.